Make a patty melt with secret sauce next time you're craving some seriously indulgent comfort food! A thin ground beef patty is layered with caramelized onions, two types of melty cheese, and a tangy secret sauce.
In a bowl, add mayonnaise, ketchup, mustard, pickle juice, paprika, and garlic powder. Mix until smooth. Set aside.
In a skillet over medium-low heat, add olive oil. When warm, add onions to pan and cook until softened and deep golden brown, about 25-30 minutes. (If onions begin to dry out or look like they're going to burn, add a splash of water to the pan and reduce the heat slightly.) Remove from heat and set aside.
In a bowl, add ground beef, salt, pepper, and worcestershire sauce. Mix to combine and form into four thin, oblong patties (shape patties to match the shape of your bread). In a skillet over medium heat, add patties and cook until browned on both sides. Remove from heat and set aside. Wipe out any excess grease from the pan.
Butter one side of each piece of bread. In a skillet over medium heat, layer your sandwiches as so: one slice of bread (buttered side down), one slice of swiss cheese, beef patty, caramelized onions, secret sauce, slice of cheddar cheese, and one slice of bread (buttered side up). Cook until golden brown on the bottom, flip, and cook until golden brown on the opposite side (this should take 1-2 minutes per side).
Secret sauce recipe will make more than enough to top four sandwiches, with leftover for dipping or enjoying again later. Store any leftover sauce in the refrigerator in a sealed container.